Circuit Description - Kenwood TKR-850 Service Manual

1. Outline
The TKR-850 is a UHF/FM repeater designed to operate in
the frequency range of 400 to 512MHz.
The unit consists of receiver, transmitter, phase-locked
loop (PLL) frequency synthesizer, and control circuits.
2. Receiver Circuit
The receiver is double conversion super-heterodyne, de-
signed to operate in the frequency range of 440 to 470MHz
(E), 450 to 480MHz (K), 480 to 512MHz (K2) or 400 to 430
MHz (K3).
The receiver circuit located in TX-RX unit (X57-696 A/2)
consists of the following : 2-1 front-end circuit, 2-2 first mixer,
2-3 IF amplifier circuit, 2-4 audio amplifier circuit, and 2-5
squelch circuit.
TX-RX unit (X57 A/2): TX-RX
IF AMP
Q3
RSSI
Q4
SW
DET W/N
NOISE DET
D5
SQL
DET
TX-RX unit (X57 B/2): Control
DEI DEO
RD
IC604
ASQ
CPU
RSSI

CIRCUIT DESCRIPTION

MCF (Wide)
XF2
IF AMP
D2 Q2
D1
MCF (Narrow)
SW
SW
XF1
W/N
W/N
44.850MHz
FM SYSTEM IC
IC9
QUD
CF1 (Wide)
SW SW
D4
CF2 (Narrow)
NOISE AMP
455kHz
Q7
W/N
AMP AMP
IC614
IC619 (A/2)
IC608 IC619 (B/2)
CODEC
AINR AOUTR
Fig. 1 Receiver circuit
2-1. Front-end Circuit
The front-end circuit consists of BPF L2, RF amplifier Q1,
and BPF L4/L5. The helical BPF covers frequency ranges 440
to 470MHz (E), 450 to 480MHz (K), 480 to 512MHz (K2) or
400 to 430MHz (K3), with a passband of 5.0MHz.
The BPF L4/L5 attenuates the unwanted signals, and
sends only the necessary signal to the first mixer DBM A1.
2-2. First Mixer
The signal from the BPF is heterodyned with the first local
oscillator signal from the PLL frequency synthesizer circuit at
the first mixer DBM (A1) to become a 44.85MHz first inter-
mediate frequency (IF) signal. The first IF signal is fed
through two monolithic crystal filters (XF2; Wide, XF1; Nar-
row) to further remove spurious signals.
44.85MHz
1st MIX BPF
L4,L5
DBM A1
IF AMP IF AMP
LPF
Q10 Q9
X1
44.395MHz
D3
LPF
RXI RXO IC615
IC622
DAC
RA
IC621
AM
SPM
TKR-850
RX ANT
BPF
RF AMP
L2
Q1
RX VCO
A3 (X58-480)
IF AMP
Q8
VCO A
VCO B
f –44.85MHz
RX
IC629
Q606
AF
SW MUTE
AMP
INV Q605
INT SP
11